In the process of oil production, if the supply of fluid from the low-yield wells is insufficient, the theoretical displacement of a single-well needs to be reduced. Since the work mode of conventional operations of the walking beam pumping unit is limited to a continuous complete-cycle motion of the crank, the theoretical displacement of the single-well can only be reduced by the following technical means.
First, the means of reducing the working strokes in the whole process, which has the following problems. Due to the reduction of strokes in the complete cycle of the pumping unit, the problem that the leakage rate of the plunger pump gradually increases will be caused. Moreover, if the motor speed is reduced by the method of frequency conversion, the driving efficiency of the motor will gradually decrease as the motor speed decreases.
Second, the means of using the interval pumping work mode, namely, the work mode of alternately performing the mode of continuous complete-cycle motion of the crank and the mode of shutdown. This kind of work mode can solve the problems of high plunger leakage rate and low motor driving efficiency, but it will cause the following new problems. In one aspect, the transition from the shutdown state to the startup state requires a staff on duty. Because there are a large number of oil wells separated from each other by long distances, the operations of shutdown and startup are labor-intensive and waste many material resources. In another aspect, since the machine is started or shut down manually, it is difficult to start and shut down the machine for more than two times within 24 hours, and no pumping for a long time will cause large fluctuations on the dynamic fluid level and downhole flow pressure. As a result, the production capacity of a single well and the development of the pay zone will be adversely affected.
Patent application No. 201510783876.2, entitled “No-pumping Operation Method for Walking Beam Pumping Unit Based on Crank Incomplete-Cycle Motion”, breaks through the technical bias that the walking beam pumping unit only has one operation mode, i.e., the crank continuous complete-cycle motion. With the incomplete-cycle swing motion of the crank, a no-pumping operation without the need of shutting down can be realized. If the traditional crank continuous complete-cycle motion is combined with the crank incomplete-cycle no-pumping motion proposed by the above patent, not only the strokes of a complete cycle are not required to be reduced, and the problems of large plunger leakage rate and low motor drive efficiency can be solved, but also manual startup and shut down operations are not required because the overground part of the pumping unit has never been shut down, thereby greatly reducing the consumption of manpower, material resources, and financial resources caused by manual startup and shut down operations on site.
However, in the practical production and operation, for the sake of safety warning, it is required to make the crank swing noticeably. While, the noticeable swings of the crank can cause the polished rod to move beyond the range of static deformation of the elasticity. As a result, it is hard to ensure the crank incomplete-cycle no-pumping motion, and the problem of theoretical displacement deviation will be caused. Meanwhile, if the area where the crank swings to a position close to a horizontal position, even a small angle rotation of the crank will also cause the polished rod to move beyond the range of the static deformation of elasticity. Accordingly, it is hard to ensure the crank incomplete-cycle no-pumping motion, and the problem of theoretical displacement deviation will be caused. In addition, when there is severe sand deposition in the oil well and the temperature is low (e.g. in the winter of Northern China), the time of the continuous no-pumping operation should not be too long, otherwise the problems of sand blocking, wax deposition, freezing blocking, and stratification are prone to occur. Based on these reasons, the crank incomplete-cycle pumping motion is essential in some special cases.
Patent application No. 201510838831.0, entitled “Dynamic Variable Stroke Operation Method for Walking Beam Pumping Unit Based on Crank Incomplete-cycle Motion”, also breaks through the technical bias that the walking beam pumping unit only has one operation mode, i.e., the mode of crank continuous complete-cycle motion. The patent realizes a variable stroke pumping operation without shutting down based on the crank incomplete-cycle swing motion. If the traditional crank continuous complete-cycle motion is combined with the crank incomplete-cycle variable stroke pumping motion, or if the traditional crank continuous complete-cycle motion, the crank incomplete-cycle no-pumping motion, and the crank incomplete-cycle variable stroke pumping motion are combined, the following advantages can also be achieved. The problems of large plunger leakage rate and low motor drive efficiency can be solved while the strokes of the complete cycle need no reduction. Also, since the overground part of the pumping unit has never been shut down, manual startup operation is not required at all, thereby greatly reducing the consumption of manpower, material resources, and financial resources caused by manual startup operation on site. What's more, the use of the crank incomplete-cycle variable stroke pumping motion, not only can overcome the problem of the theoretical displacement deviation caused because it is hard to ensure the crank incomplete-cycle no-pumping motion, but also can meet the requirement of the reasonable distribution of flowing capacity through the crank incomplete-cycle pumping motion.
However, there is no relevant technical solution for how to implement the combination of the three work modes i.e. the crank complete-cycle operation, the crank incomplete-cycle pumping operation, and the crank incomplete-cycle no-pumping operation.